idiomelon

“-- Unlike the troparion, which follows the model set by the hirmos, the idiomelon has no model.”

Hymns of the Holy Eastern Church

“If there be idiomelon, Glory, Tone 6: Upon the right hand of the Saviour there stood virgin, great sufferer and martyr (mentioned by name), arrayed in unassailable virtues and adorned with the oil of purity and with the blood of martyrdom, holding joyfully the lamp and vociferating unto Him:”

The General Menaion or the Book of Services Common to the Festivals of our Lord Jesus of the Holy Virgin and of Different Orders of Saints

“An idiomelon is a troparion that has its own melody, instead of following a heirmos (for other kinds of chant see Nilles, "Kalend.”

The Catholic Encyclopedia, Volume 4: Clandestinity-Diocesan Chancery